Antique Radio Build

Hey guys,

Hoping someone can help me here. I was recently lucky enough to get an awesome antique radio for my birthday not long ago. Its a 1947, Healing Golden Voice 501E (photos here for context -

I’m hoping to install a smart speaker into it, most likely a google nest audio -( but also want to make use of the power and volume dials on the radio, so that they control the smart speaker’s volume and power.

I’m wondering if someone can recommend the best way I might go about doing this.



Hi Shane
That unit looks in very good condition. I am a member of HRSA (Historical Radio Society of Australia) and I think some would give their right arm for that in such good condition.
They also probably have nightmares thinking about what you are going to do with it.
I don’t know anything about that speaker set up but probably the easiest place to get the radio audio and still have the level controlled by the radio knob would to connect to the centre or slider of the volume control (via a capacitor).
Cheers Bob


Hi Bob,

Thanks for getting back to me and for your interest in my little project. My lovely wife got this little beauty for me for my birthday just gone, and yes I must say it is indeed in great condition.

I understand that some might think what I’m looking to do here isn’t such a great idea, but I don’t know if the radio itself functions or indeed what sort of condition the speaker and electronics are in. Plus I thought it would be fun to add some modern functionality, and keep the vintage look and as many of the original parts in place as possible (all the cool looking vacuum tubes etc)

I’ll look to mount the Google nest audio where the existing speaker lives and then use the power supply included with it to power an LED that sites behind the tuning panel (sorry not sure of the right name). My old man is an electrician and I have a brother in law who is pretty handy with electronics, so I’ll be able to enlist help for things that I lack skill in.

Is there any chance you or someone at the HRSA might have a circuit diagram for this model? If so, I’d be very appreciative if you were able to share it with me. In return I’d be happy to make a small donation, or give you the parts that come out during the build (like the speaker for example)…



Hi Shane
I am not active in the restoration activities myself. I currently live on a residential village and my “Fiddle” space is pretty limited these days.
I believe the HRSA have some circuits but I don’t know if available to non members, they may be but I don’t know how extensive their library is.
The best way I think is if you contact the secretary directly and explain your needs and he will point you in the right direction.
His details
HRSA Secretary
Ian Batty
79 Rosebud Avenue
Victoria 3939
He will probably try to convince you to join. If you are interested in this sort of thing they publish a good very informative magazine 4 times a year called “Radio Waves”, free to members.
I hope you can get some help here
Cheers Bob


So it feels like forever since I’ve managed to give this little project some time. Finding some space to work on something with two little ones and a house t renovate sometimes isn’t easy.

In any case, I’ve been giving some thought to how I’ll make the existing knobs and dials work to control the Google Nest audio speaker. Of the 4 knobs on my old radio, its only really the volume and power knobs that I want to do anything with.

To control the speaker with the original radio knobs I figured I would use a raspberry pi zero I had lying around, and an open source api called pyChromecast. I tried this out and it can perform all the functions I want here (volume up, volume down, pause, play). A rotary encoder could be used to trigger the volume up / down commands but I’m a bit stumped on how perform the on / off function which in this case will just be pause / play.

The reason I’m stumped is because I can’t find a rotary on / off style switch like the one that’s currently in the radio. Basically it turns clock-wise and clicks ‘on’ then you turn it anti-clockwise to the off position (a 2 position rotary switch I think it would be called).

I guess I was wondering - do I need to replace the existing switch or can I use the on state to trigger and action on the Pi? I would have thought I’d need a switch that’s suitably rated for the Pi and that has a signal pin but really I’m not sure.

Hopefully someone can point me in the right direction here. Any help much appreciated.

Hi Shane,

Generally, parts in radios like that are a pair of well-matched logarithmic pots with a switch, all connected to the same knob (and all in one assembly)

For reference it’d be something like this:

As for interfacing the switch with a zero, that will be no problem, provided you use a pullup/pulldown resistor

The Zero doesn’t have any ADCs, so you’ll need an external one to read the value from the potentiometer, something like this:

If you instead wanted to go down the rotary encoder route, Adafruit make a nice part that takes all the effort of pulse-counting out of the process:

Let us know if you have more questions :slight_smile:

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Hi James,

Thanks so much for replying and for all the valuable information there. As you can tell from my questions I’m a fair bit of a novice, on the electronics side of things.

Just to clarify:

The on / off (rotary) switch on my radio only has two positions, I assume I’ll need an appropriate pull / up pull down resistor, but will I also need the ADC in order to send that change of state to the Pi. Also, how would I wire that up (generally speaking).

Hi James
I think what Shane means is the power switch is just that, it is not on the volume control, It just turns on and off

There are 4 knobs on this set and it does not seem to have any short wave bands so the knobs would probably be
The switch would control the 240V mains power but I don’t see any reason not to control a GPIO pin. Of course disconnect the mains power first.
Cheers Bob

Hi Shane

One or the other, NOT both. Some of the preceding text is a bit cloudy re this.

You should be able to send a simple HIGH or LOW to a GPIO pin on the Pi.
Cheers Bob

You can very likely use the on/off switch to trigger the Pi.

If you disconnect the wiring to the existing switch then you can simply wire one side to ground and the other to the Pi GPIO pin. When the switch is closed it takes the input for the Pi to ground - when it is open a pullup resistor on the GPIO pin pulls it towards +5v for a logic high. No ADC is needed. However please note that it’s likely that the existing switch is switching 240V so you would need to enlist the aid of an expert to ensure it was properly disconnected, or somehow prevent any possibility of someone trying to connect it to the mains. You would also need to carefully clean the switch and ensure it is operating reliably at the very low current you are switching.

Using the existing volume control will be a lot more difficult, so replacing it with a rotary encoder, as suggested above, will be a much more practical solution.


Thanks Jeff and Robert.

That helps so much! You have clarified things for me really well.

There’s no danger of the old radio being connected to the mains, as the power cord was obviously cut off before I bought it.

Hopefully I get a chance to do some tinkering in the not too distant future, so I’ let you know how it goes.


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You did ask if anyone had a circuit for the radio. I was looking around and found one for the 502E. It is likely to be similar, same rectifier (5Y3) and same output valve (6V6GT). It has four controls as does the 501E but a different cabinet. link is

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Thanks Alan for the wiring diagram. I’m sure that will come in handy.

In the end I purchased one of these rotary encoders - Rotary Encoder + Extras | Adafruit ADA377 | Core Electronics Australia ( How do I go about wiring it up to a Pi Zero? From what I’ve read online I’m a little confused about the need for resistors in the circuit (ie what size and where they should go?)

Considering I don’t need to use the push switch on the encoder, and only want to capture the signal from rotating the shaft, would something like what is shown here suffice - twistednix’s: Image (

Many thanks in advance.


Hi Shane
The rotary encoder will output 2 switches 90º apart. normally pulled to ground so pull up resistors are required. Without looking at that link I would guess that to be the case. The output from these two switches has to be decoded to get a count and rotation direction. The decoding will either increment or decrement the count.

The little board that James linked earlier might be the way to go. I don’t have one but it would seem the on board smarts do all the encoding and communicate the output to a host device via I2C. This is probably a string of numbers going up or down as the encoder is rotated. It is possible you may get a number change of “4” per encoder indent (or click) so if you want an increase (or decrease) of “1” simply divide by 4. As I say I don’t have one so am not sure.
Be aware though that unless the smarts include some sort of non volatile memory the encoder will start up with an output of “0” in other words it will not remember the volume setting at last switch off.
I would be interested in this aspect so maybe someone at Core can enlighten us. I might post this question on the product thread.
Cheers Bob
EDIT. Just had a look at that linked video. I seem that the encoder increments and decrements in "1"s as it stopped sometimes on a number not divisible by 4. Unless the host device is doing that before displaying, there is no way of knowing. As the woman in the video talks like a machine gun and the man can’t get a word in anywhere I find I cannot understand a word being said but that is probably me.


Hi Bob,

Thanks again for taking the time to help and I apologise again for my lack of knowledge when it comes to electronics.

To do what I need to do for the volume knob I think I have found a python class that will interpret the signals from the rotary encoder - GitHub - bobrathbone/pirotary: Raspberry PI Rotary Swich classes as it moves in either a clock wise (volume up) or anti-clock wise direction (volume down).

Many similar examples I’ve seen, simply wire the ground pin on the encoder to a ground pin on the Pi, and the A and B to separate GPIO pins. This all seems pretty straight forward, but what I’m not clear on is the need for resisters and where to put them. James & Bob have both stated that I would need a pull up resistor. How would I go about wiring that up here?

Thanks again.

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Hi Shane

From “A” and “B” to VCC. (5V or 3.3V depending on RPi requirement). The software may take care of switch debounce but if you get erratic behaviour you may need a filter. Let us know and I will post a sketch. Also the GPIO may have internal pull-ups which you can enable similar to Arduino. I don’t know. If you need an external debounce filter you won’t be able to use the internal pull ups.
I may be confusing the issue here so just use external pull ups anyway, 10kΩ is a good all round value.
Cheers Bob

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Hi guys,

Been a little while since my last update on this. Thanks again for all the help.

As I think I might have mentioned I picked up some rotary encoders, and managed to get things working as I’d hoped - for the volume control anyways. It was simply a matter of wiring the Ground Pin on the Encoder to a Ground Pin on my Pi Zero then wiring both A and B outputs to a separate GPiO pin (no resisters used in this case).

Then using this great tutorial, and the associated python library I was able to read the state of the rotary encoder when turned clockwise / anti-clockwise.

Taking this a step further, I also managed to tie in the use of the pychromecast module such then when the encoder was turned clockwise, the command was triggered to turn the volume up, and down when turned anti clock wise.

So I was pretty happy with that, but I evidently have a few more challenges in front of me before this all comes together. I’ll no doubt ask a lot more silly questions of you good folk - like wiring up the on / off switch such that it can trigger some LEDs.

But that’ll be for another day. Thanks again.


Hi Shane.
Great news. The switch debounce is probably taken care of in the Python library so no filter or pull up resistors needed.
Cheers Bob